Optical transmission device, method for manufacturing same, and optical transmission module

ABSTRACT

According to one embodiment, a via holds an optical fiber and has an opening in at least a first surface of a silicon substrate. An interconnect is provided at a second surface of the silicon substrate and connected to an optical semiconductor element. Side-surface electrodes are provided at a third surface of the silicon substrate. The third surface is other than the first surface and the second surface of the silicon substrate. At least a portion of the side-surface electrodes is connected to the interconnect. At least a portion of the side-surface electrodes have different lengths along the third surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-174033, filed on Sep. 18, 2018; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an optical transmissiondevice, a method for manufacturing an optical transmission device, andan optical transmission module.

BACKGROUND

Optical transmission modules are used in high-speed local area networks,data center wiring, etc., and are being developed for higher speeds,downsizing, and higher density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing an optical transmissiondevice of a first embodiment;

FIGS. 2A and 2B are detailed explanation views of side-surfaceelectrodes of the optical transmission device of the first embodiment;

FIGS. 3A to 3D are schematic configuration views of the opticaltransmission device of the first embodiment;

FIG. 4 is a schematic cross-sectional view of an optical transmissionmodule of the first embodiment;

FIG. 5 to FIG. 8 are schematic top views showing a method formanufacturing the optical transmission device of the first embodiment;

FIGS. 9A and 9B are schematic configuration views of an opticaltransmission device of a second embodiment; and

FIG. 10 is a schematic top view showing a method for manufacturing theoptical transmission device of the second embodiment.

DETAILED DESCRIPTION

According to one embodiment, an optical transmission device includes avia, at least one optical semiconductor element, an interconnect, and aplurality of side-surface electrodes. The via holds an optical fiber andhas an opening in at least a first surface of a silicon substrate. Theoptical semiconductor element is provided on a second surface of thesilicon substrate opposing the first surface in a region where the viaholding the optical fiber is formed. Or the optical semiconductorelement is provided on the via holding the optical fiber on the secondsurface side of the silicon substrate opposing the first surface. Theinterconnect is provided at the second surface of the silicon substrateand connected to the optical semiconductor element. The side-surfaceelectrodes are provided at a third surface of the silicon substrate. Thethird surface is other than the first surface and the second surface ofthe silicon substrate. At least a portion of the plurality ofside-surface electrodes is connected to the interconnect. At least aportion of the plurality of side-surface electrodes have differentlengths along the third surface.

Embodiments are described below with reference to the drawings asappropriate. For convenience of description, the scale in each drawingis not always accurate; and relative positional relationships, etc., maybe used. The same or similar components are marked with the samereference numerals.

The downsizing of an optical transmission module has been problematicbecause a marker for recognizing the side-surface electrode (theperpendicular-surface electrode) arrangement of an optical transmissiondevice of a direct-optical-fiber-connection optical element, adirect-optical-fiber-connection optical element mounting substrate,etc., has not been provided; and automatic recognition of thearrangement of the side-surface electrodes could not be performed.

Embodiments of the invention are directed to provide an opticaltransmission device, a method for manufacturing the optical transmissiondevice, and a compact and inexpensive optical transmission module usingthe optical transmission device in which a marker for easily recognizingthe arrangement of the side-surface electrodes is formed.

Optical transmission devices such as the direct-optical-fiber-connectionoptical element or the direct-optical-fiber-connection optical elementmounting substrate of Patent Literature 1 to 3, etc., have been proposedto realize a broadband interconnect by configuring a high densityoptical transmission array by extremely downsizing an opticaltransmission module capable of high-speed transmission. In particular,by integrating optical elements in a Si substrate and by performing thepositional alignment and the holding of the optical fibers using the Sisubstrate, Patent Literature 3 can realize an optical coupling moduleusing the minimum configuration of only the optical elements (theintegrated optical elements) and the optical fibers.

Generally, optical elements, and in particular, light-emitting elementsinclude a compound semiconductor material (GaInAsP, AlGaAs, AlGaInAs,InGaN, etc.); and the crystal growth substrate of the element oftenincludes a compound semiconductor (InP, GaAs, GaN, etc.) as well. Manycompound semiconductors are cleavable due to crystal anisotropy and aredifficult to use as a mechanical holder directly fixing the opticalfiber due to damage occurring easily due to impact and stress.

However, in Patent Literature 3 recited above, a configuration ispossible in which the optical elements are integrated in the Sisubstrate; and the optical fibers are pseudo-directly fixed to theoptical elements by the Si substrate also holding the optical fiber.Because the substrate is Si, semiconductor manufacturing technology isapplicable; and cost reduction by mass production is possible. By theapplication of semiconductor manufacturing technology, the high densityarray of the optical elements is formed easily; and a high densityoptical transmission module array can be configured by combining with ahigh density optical fiber array using a staggered arrangement of theoptical fibers, etc. In other words, not only is a substantially opticalfiber-attached optical element realizable, but also a large-capacitymulti-core optical transmission module having higher density up to thephysical limit of the arrangement of the optical fibers can beconfigured.

Such an optical transmission module is configured by electricallyconnecting a drive IC to the optical transmission device includingoptical elements or integrated optical elements; but if the drive IC isintegrated in the Si substrate where the optical elements areintegrated, the dedicated chip surface area increases for the drive IC;and it is often that the cost increases drastically due to yielddecrease caused by processes other than the unique processes, preventionmeasures for contamination between composite materials, etc. Therefore,generally, the drive IC is manufactured as a separate chip; and theintegration is performed using mounting technology.

Although a mounting configuration of the optical transmission module ispossible in which the optical transmission device is stack-mounted withthe drive IC, an external force is applied to the optical transmissiondevice recited above via the optical fiber; therefore, a stack-mounteddrive IC must mechanically receive the external force; and such amounting configuration is not desirable due to degradation and/or damageof the drive IC.

Therefore, as shown in the embodiments described below, mountingconfigurations are widely used in which the drive IC and the opticaltransmission device or the optical coupling module are fixed in onemounting unit or module substrate so that stress is not transmitted; andthe drive IC and the optical transmission device or the optical couplingmodule are electrically connected by, for example, a bonding wire,plated wiring, etc. In such a case, by configuring the optical fiber tobe drawn out in a direction perpendicular to the mounting unit (or themodule substrate) and by fixing the optical element integration surfaceof the optical transmission device and the circuit surface of the driveIC to face the same direction, the electrical connection is easy; butthe component mounting height that generally needs to be thinner becomesextremely high because the optical fiber draw-out is in the directionperpendicular to the substrate when the optical transmission module ismounted to a printed circuit board, etc.

Therefore, as described below, side-surface electrodes are provided inthe optical transmission device; the placing on the mounting unit or themodule substrate is performed so that the integration surface of theoptical element is perpendicular to the mounting surface; therefore, theoptical fiber draw-out direction can be parallel to the mounting surface(providing a low component mounting height); and the electricalconnection is easy because the optical transmission device and theelectrical connection surface of the drive IC are in the same direction.

When integrating optical elements in a Si substrate by semiconductormanufacturing technology and then forming side-surface electrodes,generally, the side-surface electrodes are formed individually aftersingulating the optical transmission devices; or the side-surfaceelectrodes are formed by forming the electrodes to be buried in thewafer state and by halving the electrodes when singulating; but theformer is poor for mass production and prohibitively expensive; and forthe latter, the shape discrimination of the side-surface electrodes isdifficult; in particular, for higher pin-count side-surface electrodes,etc., problems occur due to misjudgment of the corresponding connectionsin the mounting process, that is, defective parts occur easily.

Therefore, a method for identifying the arrangement information of theside-surface electrodes may be considered in which the width and/or thepitch of the electrodes is intentionally changed when forming theside-surface electrodes in the optical transmission device; but in sucha case, the arrangement pitch of the electrodes is not constant;therefore, the uniformity of the mounting interconnects (e.g., wirebonding) degrades; characteristic fluctuation, asymmetry, etc., of thewiring and/or the electrodes occurs easily; for example, jitter due toasymmetry of the wiring lengths of differential wiring, skew betweenoptical transmission channels, etc., may occur. Accordingly, it isdesirable to provide the side-surface electrodes of the opticaltransmission device with uniform widths and pitches; and a method foreasily recognizing the arrangement information of such side-surfaceelectrodes is desirable.

First Embodiment

FIG. 1 is a schematic perspective view showing an optical transmissiondevice 51 of a first embodiment.

The optical transmission device 51 includes a silicon substrate 1, anoptical element 2, a first electrode group 21, a second electrode group22, and an interconnect 3. The silicon substrate 1 has an opticalelement surface 1 a, a first side surface 1 b, a second side surface 1c, and a via 5 provided in the surface opposing the optical elementsurface 1 a. The optical element 2 is, for example, an opticalsemiconductor element such as a light-emitting device, a photodetector,etc.

At least one optical element 2 is provided in the optical elementsurface 1 a. In the example shown in FIG. 1, multiple optical elements 2are integrated in the optical element surface 1 a of the siliconsubstrate 1. For example, the optical element surface 1 a is formed in arectangular configuration; and the multiple optical elements 2 arearranged along the longitudinal direction of the optical element surface1 a.

The via 5 has an opening at the surface of the silicon substrate 1 onthe side opposite to the optical element surface 1 a and is, forexample, a blind via extending toward the optical element surface 1 afrom the opening. The optical element 2 is provided at a positionopposing the bottom surface of the via (the blind via) 5. For example,the multiple vias 5 are arranged along the longitudinal direction of theoptical element surface 1 a to correspond to the multiple opticalelements 2. As in Patent Literature 2, the via 5 may be a through-via;and the optical element 2 may be an optical element chip that isseparately formed and placed so that the optical element is electricallyconnected to the interconnect 3 of the Si substrate 1.

The first side surface 1 b and the second side surface 1 c of thesilicon substrate 1 cross the optical element surface 1 a. For example,the first side surface 1 b and the second side surface 1 c areorthogonal to the optical element surface 1 a. The second side surface 1c is provided on the side opposite to the first side surface 1 b. Forexample, the first side surface 1 b and the second side surface 1 c alsoare formed in rectangular configurations.

The first electrode group 21 is provided in the first side surface 1 b.The first electrode group 21 includes multiple side-surface electrodes 4a and 4 b. The multiple side-surface electrodes 4 a and 4 b areseparated from each other and are arranged along the longitudinaldirection of the first side surface 1 b at, for example, a uniformpitch. For example, the first electrode group 21 may be floatingelectrodes not electrically connected to the interconnects 3. Also, itis not always necessary to provide the first electrode group 21; and thefirst electrode group 21 may be omitted.

The second electrode group 22 is provided in the second side surface 1c. The second electrode group 22 also includes the multiple side-surfaceelectrodes 4 a and 4 b. The multiple side-surface electrodes 4 a and 4 bare separated from each other and are arranged along the longitudinaldirection of the second side surface 1 c at, for example, a uniformpitch.

The interconnect 3 is provided at the optical element surface 1 a. Theinterconnect 3 electrically connects the optical element 2 and thesecond electrode group 22.

FIG. 2A is an enlarged perspective view of the second electrode group 22connected to the interconnect 3.

FIG. 2B is an enlarged cross-sectional view of the second electrodegroup 22.

The first electrode group 21 is configured similarly to the secondelectrode group 22.

The first electrode group 21 and the second electrode group 22 areformed by providing an insulating film 6 on the side surfaces and thebottom surfaces of the multiple vias (broken lines) 11 provided in thesilicon substrate 1 and by filling the vias 11 with a metal such as Au,Ni, Cu, etc., by, for example, plating; and the side-surface electrodes4 a and 4 b can be formed by cutting the metal in the via depthdirection. As shown in FIG. 1, the side-surface electrodes 4 a and 4 bof the first electrode group 21 are exposed at the first side surface 1b; and the side-surface electrodes 4 a and 4 b of the second electrodegroup 22 are exposed at the second side surface 1 c. The first electrodegroup 21 may not be formed by positioning the first electrode group 21inside the dicing street (the cutting width) when cutting in the viadepth direction described above. One end of each of the side-surfaceelectrodes 4 a and 4 b is exposed at the optical element surface 1 a.

The multiple vias 11 for forming the side-surface electrodes 4 a and 4 bare not so-called through-vias (TSVs (Through Silicon Vias)), but arenon-through vias (blind vias) having openings at the optical elementsurface 1 a. The vias 11 extend in the direction along the via 5 forholding the optical fiber from the surface opposite to that of the via5. The multiple vias 11 include a first blind via 11 a and a secondblind via 11 b having mutually-different depths.

The insulating film 6 insulates the side-surface electrodes 4 a and 4 band the silicon substrate 1 and is, for example, a SiO₂ film. Theinsulating film 6 is formed also at the optical element surface 1 a; andthe interconnect 3 is formed on the insulating film 6. Hereinbelow, theinsulating film 6 is not illustrated for simplicity of the drawings.

FIG. 3A is a top view of the optical transmission device 51 of the firstembodiment.

FIG. 3B is an A-A′ cross-sectional view of FIG. 3A.

FIG. 3C is a side view of the second side surface 1 c of FIG. 3A.

FIG. 3D is a B-B′ cross-sectional view of FIG. 3A.

As described below, the depths of the multiple vias 11 for forming theside-surface electrodes 4 a and 4 b are set to be different. Thereby,the length of the side-surface electrode 4 a and the length of theside-surface electrode 4 b are different from each other. Here, thelengths of the side-surface electrodes 4 a and 4 b are the lengths inthe direction along the depth of the via 11. The length of theside-surface electrode 4 a is shorter than the length of theside-surface electrode 4 b. One end of the side-surface electrode 4 aand one end of the side-surface electrode 4 b are positioned at theoptical element surface 1 a. The other end of the side-surface electrode4 a and the other end of the side-surface electrode 4 b are positionedat the bottom surfaces of the vias 11. The length from the one end tothe other end of the side-surface electrode 4 a is shorter than thelength from the one end to the other end of the side-surface electrode 4b.

As shown in FIG. 1 and FIG. 3A, the width of the side-surface electrode4 a and the width of the side-surface electrode 4 b are the same in thearrangement direction of the second electrode group 22 (or the firstelectrode group 21).

In a direction orthogonal to the arrangement direction of the secondelectrode group 22 (or the first electrode group 21), the width (thelength) of the side-surface electrode 4 b is larger (longer) than thewidth (the length) of the side-surface electrode 4 a. The differencebetween the lengths of the side-surface electrode 4 a and theside-surface electrode 4 b is set to a length difference that can bedistinguished by an image recognition device and/or microscopy and isset to be, for example, not less than 2 times the minimum resolution ofthe image recognition device, and favorably not less than 10 times theminimum resolution of the image recognition device.

For both the second electrode group 22 and the first electrode group 21in the example shown in FIG. 1, the long side-surface electrode 4 b isprovided second from the left when viewed from the upper surface andsecond and third from the right when viewed from the upper surface.Several short side-surface electrodes 4 a are connected to the opticalelements 2 via the interconnects 3. The long side-surface electrode 4 bis a marker particularly for identifying the arrangement of the secondelectrode group 22; and the arrangement information can be indicated bythe positions and/or the continuous number of the side-surfaceelectrodes 4 b.

For example, in FIG. 3C, the long side-surface electrodes 4 b arearranged laterally asymmetrically with respect to thearrangement-direction center of the electrode group; one longside-surface electrode 4 b is disposed on the left side; and two longside-surface electrodes 4 b are disposed on the right side. Thereby, itcan be identified whether or not the placement position relationship ofthe optical transmission device 51 is correct; and the case where theorientation of the optical transmission device 51 is reversed in theplane or flipped can be discriminated easily because the lateralarrangement relationship of the side-surface electrodes 4 b is reversed.Also, in the case where the optical transmission device 51 is flippedand the orientation is reversed, the formation positions of theside-surface electrodes 4 b in the silicon substrate 1 are reversedvertically; therefore, the discrimination is possible using the numberand the vertical positions of the long side-surface electrodes 4 b.

Of course, the details of the side-surface electrodes 4 a can berecognized from the relative relationship with respect to theside-surface electrodes 4 b; for example, the optical element electrodepositions can be recognized and wire connection can be performedautomatically by pre-registering, in a wire bonder, etc., theinformation that eight electrodes of the optical elements 2 are arrangedin the right direction from one side-surface electrode 4 b.

FIG. 4 is a schematic cross-sectional view of an optical transmissionmodule 100 according to the first embodiment.

The optical transmission module 100 includes a module substrate 8, theoptical transmission device 51 recited above mounted on the modulesubstrate 8, and a semiconductor element 9 mounted on the modulesubstrate 8. The semiconductor element 9 is, for example, a drive IC(Integrated Circuit) driving the optical element 2.

In the optical transmission module 100, the first side surface 1 b wherethe first electrode group 21 is provided is mounted to oppose a mountingsurface 8 a of the module substrate 8. The second side surface 1 c wherethe second electrode group 22 electrically connected to the opticalelements 2 is provided faces upward from the mounting surface 8 a of themodule substrate 8. The side-surface electrodes 4 a of the secondelectrode group 22 and the semiconductor element 9 are electricallyconnected by wires 10. Accordingly, the optical elements 2 areelectrically connected to the semiconductor element 9 via theinterconnects 3, the side-surface electrodes 4 a, and the wires 10.

An optical fiber 7 is held in the via 5 of the silicon substrate 1.Light propagates between the optical fiber 7 and the optical element 2via a thinned portion 32 of the silicon substrate 1 between the via 5and the optical element surface 1 a.

The configuration shown in FIG. 4 is effective in the case where thesemiconductor element 9 and the optical transmission device 51 are fixedon the module substrate 8 and the wire connection between thesemiconductor element 9 and the optical transmission device 51 isperformed by an automatic wire bonder, etc. By using the opticaltransmission device 51 of the embodiment, mass production usingautomatic assembly apparatuses is possible; and an extremely inexpensiveoptical transmission module 100 can be configured because thearrangement information recognition error of the side-surface electrodes4 a and 4 b is small and the manufacturing yield is high.

In the optical transmission module 100, the second side surface 1 cwhere the second electrode group 22 of the optical transmission device51 is provided may be mounted toward the mounting surface 8 a of themodule substrate 8; the semiconductor element 9 also may be mountedtoward the mounting surface 8 a of the module substrate 8; and thesecond electrode group 22 of the optical transmission device 51 and theelectrodes of the semiconductor element 9 may be electrically connectedby wiring provided in the mounting surface 8 a of the module substrate8. Also, a so-called fan-out wafer level package may be used in whichthe second side surface 1 c where the second electrode group 22 of theoptical transmission device 51 is provided and the surface where theelectrodes of the semiconductor element 9 are formed are temporarilybonded to a dummy substrate; the optical transmission device 51 and thesemiconductor element 9 are molded by a resin; the dummy substrate ispeeled off; and rerouting of the optical transmission device 51 and thesemiconductor element 9 is formed by plating, etc.

Also, in such an optical transmission module, the error of thearrangement information recognition can be smaller by using theside-surface electrodes 4 a and 4 b for positional alignment whenplacing the optical transmission device 51 on the wiring of the modulesubstrate 8 and for pattern alignment when providing the rerouting onthe optical transmission device 51; therefore, the manufacturing yieldalso is high; and an extremely inexpensive optical transmission module100 can be configured.

Thus, according to the embodiment, it is possible to recognize theelectrode arrangement information, etc., by observing only theside-surface electrodes 4 a and 4 b; and a high pin-count connection ofthe side-surface electrodes 4 a and 4 b can be performed reliablywithout modifying the width (the width in the arrangement direction)and/or the pitch of the side-surface electrodes 4 a and 4 b. Also,optical transmission module manufacturing is possible using automaticapparatuses; and the supply of an inexpensive high density multi-coreoptical transmission module is possible.

Second Embodiment

FIG. 5 to FIG. 8 are schematic top views showing a method formanufacturing the optical transmission device 51 of the firstembodiment.

FIG. 5 shows the state in which the multiple optical elements 2 areformed in the first major surface (the optical element surface) is ofthe silicon substrate 1.

The optical element 2 is, for example, a surface-emitting semiconductorlaser and includes a p-type region 2 a and an n-type region 2 b. Forexample, the surface-emitting semiconductor laser is formed by crystalgrowth of a compound semiconductor multilayer film including a p-typesemiconductor multilayer mirror, a light-emitting layer, and an n-typesemiconductor multilayer mirror on a compound semiconductor substrate,directly bonding the compound semiconductor multilayer film on thecleaned first major surface (the optical element surface) 1 a of thesilicon substrate 1, performing heat treatment, and removing thecompound semiconductor substrate and the unnecessary regions of thecompound semiconductor multilayer film by etching. A p-type ohmicelectrode and an n-type ohmic electrode also are formed in thesurface-emitting semiconductor laser.

FIG. 6 shows the state in which the multiple blind vias 11 are formed inthe silicon substrate 1.

The blind vias 11 have openings at the first major surface (the opticalelement surface) 1 a. The multiple blind vias 11 are arranged along anX-direction. The multiple blind vias 11 that are arranged along theX-direction form one via column. Multiple via columns are arranged alsoin a Y-direction orthogonal to the X-direction. The multiple opticalelements 2 are arranged along the X-direction in the region between thevia column and the via column.

The multiple blind vias 11 include the first blind via 11 a and thesecond blind via 11 b. The second blind via 11 b is deeper than thefirst blind via 11 a.

The arrangement pitch in the X-direction of the multiple blind vias 11 aand 11 b is constant; and the opening width in the X-direction of thefirst blind via 11 a and the opening width in the X-direction of thesecond blind via 11 b are the same. For example, the blind vias 11 a and11 b that have opening widths in the X-direction of 80 μm are formed ata pitch along the X-direction of 125 μm.

However, unlike the opening width in the X-direction of the first blindvia 11 a and the opening width in the X-direction of the second blindvia 11 b, the opening width in the Y-direction of the second blind via11 b is wider than the opening width in the Y-direction of the firstblind via 11 a. For example, the opening width in the Y-direction of thefirst blind via 11 a is 80 μm; and the opening width in the Y-directionof the second blind via 11 b is 150 μm.

The multiple blind vias 11 that include the first blind via 11 a and thesecond blind via 11 b are formed simultaneously by dry etching. Forexample, the multiple blind vias 11 are formed by a so-called Boschprocess. The Bosch process is dry etching in which the three steps ofisotropic etching of silicon, depositing a protective film, andanisotropic etching of the silicon (removing the protective film at thebottom surface of openings) are repeated; and the Bosch process realizesa via perpendicular to the silicon substrate at a high speed and a highaspect ratio. For example, SF₆ gas is used to etch the silicon; and, forexample, C₄F₈ gas is used to deposit the protective film.

As recited above, for example, a photoresist mask is formed to have afirst opening of 80 μm×80 μm at the position where the first blind via11 a is to be formed, and a second opening of 80 μm×150 μm at theposition where the second blind via 11 b is to be formed; and the firstblind via 11 a is etched by the Bosch process recited above to a depthof, for example, 80 μm. At this time, the opening surface area of thesecond blind via 11 b is larger than that of the first blind via 11 a;therefore, the etching of the second blind via 11 b progresses moreeasily than for the first blind via 11 a; and the second blind via 11 bis etched to a depth of about 90 to 100 μm.

By performing isotropic etching to a depth of, for example, 20 μm beforethe Bosch process recited above and then continuing etching with theBosch process to a total depth of 80 μm (the depth of the first blindvia 11 a), an opening spreading portion 31 that has a taperedconfiguration can be formed in the opening edge of the blind via 11 asshown in FIG. 2A. The tapered opening spreading portion 31 can preventelectrical disconnects at the connection portion between theinterconnect 3 formed in the first major surface (the optical elementsurface) 1 a of the silicon substrate 1 and a buried electrode 4 insidethe blind via 11 when forming the interconnect 3 shown in FIG. 7.Subsequently, the photoresist is removed; and the formation of the blindvia 11 is complete.

In this state, the insulating film 6 described above (e.g., the SiO₂film) is formed on the entire surface of the exposed surface of thesilicon substrate 1 to have a flat-portion thickness of, for example,400 nm; further, for example, a seed layer is formed by forming 30 nm ofTi, 10 nm of Pt, and 20 nm of Au on the entire surface. Subsequently, aphotoresist is formed in the regions other than the blind vias 11; and,for example, the blind vias 11 are filled with Au by performing Auplating. Thereby, as shown in FIG. 7, the electrodes 4 are formed insidethe blind vias 11. Thereafter, the photoresist is removed; and polishingof the Au plating protrusions is performed if the unevenness of the Auplating is severe. Then, the seed layer that is exposed by the removalof the photoresist is removed by etching.

Then, contact holes are formed in the insulating film 6 on the p-typeohmic electrodes and the n-type ohmic electrodes of the optical elements2; for example, 30 nm of Ti, 10 nm of Pt, and 300 nm of Au are formed onthe entire surface; and a photoresist pattern is formed and etching isperformed so that the optical element interconnects 3 and the electrodes4 filled into the blind vias 11 remain. Thereby, the p-type ohmicelectrodes and the n-type ohmic electrodes of the optical elements 2 areelectrically, connected respectively to the electrodes 4 inside theblind vias 11.

Then, the silicon substrate 1 is cut at the position of the singledot-dash line of FIG. 8 extending to cross, in the X-direction, thecolumn of the electrodes 4 inside the blind vias 11 arranged in theX-direction; and the multiple optical transmission devices aresingulated. For example, the singulation is performed using bladedicing. The electrodes 4 inside the blind vias 11 are subdivided intotwo in the Y-direction. Also, the first side surface 1 b and the secondside surface 1 c of the silicon substrate 1 described above are formedby the dicing.

By subdividing the electrodes 4 inside the blind vias 11 into two in theY-direction, two cross sections are made from one electrode 4. One crosssection is exposed at the first side surface 1 b; and the electrodes atthe one cross section are included in the first electrode group 21. Theother cross section is exposed at the second side surface 1 c; and theelectrodes at the other cross section are included in the secondelectrode group 22. At this time, as described above, the firstelectrode group 21 can be caused to disappear by adjusting the cuttingposition and the cutting width of the dicing, etc.

The side-surface electrodes 4 a are obtained by subdividing theelectrodes 4 provided inside the first blind vias 11 a; and the longside-surface electrodes 4 b that are longer (longer in the directionalong the depth of the blind vias 11) than the side-surface electrodes 4a are obtained by subdividing the electrodes 4 provided inside thesecond blind vias 11 b that are deeper than the first blind vias 11 a.

According to the embodiment, multiple types of the blind vias 11 a and11 b having different depths can be formed in one process; and byforming the electrodes inside the blind vias 11 a and 11 b, theside-surface electrodes 4 a and 4 b can be formed simultaneously to havethe multiple types of lengths recited above even though the pitch in thearrangement direction and the width in the arrangement direction areconstant. Accordingly, mass production using semiconductor manufacturingtechnology is possible; the side-surface electrodes 4 a and 4 b thathave the multiple types of lengths can be formed in one electrodeprocess; therefore, the arrangement information marker of theside-surface electrodes 4 a and 4 b can be formed without a special costincrease.

Third Embodiment

FIG. 9A is a top view of an optical transmission device 52 of a thirdembodiment.

FIG. 9B is a side view of the second side surface 1 c of the opticaltransmission device 52.

FIG. 10 is a top view showing a method for manufacturing the opticaltransmission device 52.

FIG. 9A corresponds to the top view of FIG. 3A of the first embodiment;FIG. 9B corresponds to the side view of FIG. 3C of the first embodiment;and FIG. 10 corresponds to the top view of FIG. 8 of the firstembodiment. The corresponding components of the first embodiment and thethird embodiment are marked with the same reference numerals.

In the embodiment, the electrode material for forming the side-surfaceelectrodes 4 a and 4 b does not completely fill the interiors of theblind vias 11; and electrode unfilled portions (cavity portions) 12 areformed inside the blind vias 11.

Recesses 13 that are concave from the first side surface 1 b and thesecond side surface 1 c are formed by cutting the blind vias 11including the cavity portions 12 at the single dot-dash line positionshown in FIG. 10. The recesses 13 have openings at the first sidesurface 1 b and the second side surface 1 c.

One end of the recess 13 is an open end that is open at the opticalelement surface 1 a; and the other end of the recess 13 is a plugged endpositioned inside the silicon substrate 1. The side-surface electrodes 4a and 4 b are provided at the bottom surfaces and the side surfaces(including the end surfaces of the plugged ends) of the recesses 13.

The depth of the recess 13 is the distance between the opening and thebottom surface; and the depth direction of the recess 13 (in FIG. 9A,the vertical direction) is orthogonal to the depth direction of theblind via 11 (in FIG. 9B, the vertical direction). In FIG. 9B, the depthdirection of the recess 13 is a direction orthogonal to the pagesurface.

As shown in FIG. 9A, the multiple recesses 13 that are formed in thefirst side surface 1 b have recesses having different depths. On theother hand, the depth is the same for all of the recesses 13 formed inthe second side surface 1 c. However, as shown in FIG. 9B, the multiplerecesses 13 that are formed in the second side surface 1 c have recesseshaving different lengths. The lengths of the recesses 13 correspond tothe depths of the blind vias 11. The multiple recesses 13 that areformed in the first side surface 1 b also include recesses havingdifferent lengths. The side-surface electrodes 4 b are provided in therecesses 13 that are longer than the recesses 13 in which theside-surface electrodes 4 a are provided.

In the first embodiment shown in FIG. 3A, the side-surface electrodes 4a and 4 b have substantially the same outer surface as the side surfaces1 b and 1 c of the silicon substrate 1; but in the third embodiment, theside-surface electrodes 4 a and 4 b are concave from the side surfaces 1b and 1 c of the silicon substrate 1. The metal filling of the blindvias 11 requires an extremely thick plating process; therefore, the costof the plating process easily becomes a large burden; and problems occureasily such as incomplete filling due to fluctuation of the platingfilling and yield decrease due to abnormal plating. The third embodimentcan avoid such problems. Namely, a plating thickness of about 100 μm isnecessary for the plating filling of the blind vias 11 described in thesecond embodiment; and the difference between the plating fillingconfigurations occurring easily due to the different depths of the firstblind via 11 a and the second blind via 11 b, etc., can be eliminated.

In the formation of the side-surface electrodes 4 a and 4 b shown inFIGS. 9A and 9B, for example, the Au plating on the seed layer describedabove is formed to be drastically thin, e.g., about 2 μm. When theside-surface electrodes 4 a and 4 b are formed by cutting, the Authickness of the side-surface electrodes 4 a and 4 b is 2 μm or more andis a sufficient thickness as the electrode metal.

However, in the case where the side-surface electrodes 4 a and 4 b areconnected to the semiconductor element (the drive IC) 9, a power supply,a ground potential, etc., by an electrical connection such as wirebonding, etc., for the blind vias 11 shown in FIG. 3A, the bottomsurfaces of the side-surface electrodes 4 a and the bottom surfaces ofthe side-surface electrodes 4 b may not be uniform; and the wire bondingmay be difficult.

Therefore, even in the case where the depths of the blind vias 11 a and11 b are different, in the third embodiment, the bottom surface heightsof the multiple recesses 13 obtained by cutting the multiple blind vias11 a and 11 b as shown in FIG. 9A are caused to match so that the bottomsurface heights of the side-surface electrodes 4 a and 4 b are uniform.In the example shown in FIG. 9A, the bottom surface heights of themultiple recesses 13 formed in the second side surface is that arewire-bonded match.

However, because the side-surface electrodes 4 a and 4 b function asmarkers for identifying the arrangement of the second electrode group 22as shown in FIG. 9B, it is necessary for the depth of the first blindvia 11 a and the depth of the second blind via 11 b to be different. Inother words, it is necessary for the opening width of the first blindvia 11 a in the direction orthogonal to the arrangement direction to bedifferent from the opening width of the second blind via 11 b in thedirection orthogonal to the arrangement direction.

Therefore, an offset d such as that shown in FIG. 9A is provided at theedge positions of the openings of the blind vias 11 a and 11 b which arethe recesses 13 having the openings at the first side surface 1 b thatare not wire-bonded. For example, as described above, in the case wherethe opening size of the first blind via 11 a is 80 μm×80 μm and theopening size of the second blind via 11 b is 80 μm×150 μm, the offset dshown in FIG. 9A can be set to 70 μm.

FIG. 10 corresponds to the process of FIG. 8 of the first embodiment. Asshown in FIG. 10, one end in the Y-direction of the opening of the firstblind via 11 a and one end in the Y-direction of the opening of thesecond blind via 11 b are aligned along the X-direction. On the otherhand, the position of the other end in the Y-direction of the opening ofthe first blind via 11 a is shifted in the Y-direction with respect tothe position of the other end in the Y-direction of the opening of thesecond blind via 11 b. Thus, the opening width in the Y-direction of thesecond blind via 11 b is set to be wider than the opening width in theY-direction of the first blind via 11 a. Accordingly, the second blindvia 11 b can be set to be deeper than the first blind via 11 a bysimultaneously performing dry etching of the first blind via 11 a andthe second blind via 11 b in a Bosch process.

By cutting at the position of the single dot-dash line shown in FIG. 10,the depths of the multiple recesses 13 of the side-surface electrodes 4a and 4 b, which are connected to the optical elements 2 via theinterconnects 3 and are the object of the wire bonding, can be uniformwithin, for example, about 5 μm. Accordingly, the side-surfaceelectrodes 4 a and 4 b are applicable as electrical connection pads ofwire bonding, etc., without problems.

Also, pattern recognition of the side-surface electrodes 4 a and 4 b ispossible using the difference of the lengths of the recesses 13 (thedepths of the blind vias 11) shown in FIG. 9B that appear at the crosssections.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modification as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An optical transmission device, comprising: a viaholding an optical fiber and having an opening in at least a firstsurface of a silicon substrate; at least one optical semiconductorelement, the optical semiconductor element being provided on a secondsurface of the silicon substrate opposing the first surface in a regionwhere the via holding the optical fiber is formed, or the opticalsemiconductor element being provided on the via holding the opticalfiber on the second surface side of the silicon substrate opposing thefirst surface; an interconnect provided at the second surface of thesilicon substrate and connected to the optical semiconductor element;and a plurality of side-surface electrodes provided at a third surfaceof the silicon substrate, the third surface being other than the firstsurface and the second surface of the silicon substrate the plurality ofside-surface electrodes including a first side-surface electrodeconnected to the optical semiconductor element through the interconnectand a second side-surface electrode not connected to the opticalsemiconductor element, a length of the first side-surface electrodealong the third surface being different from a length of the secondside-surface electrode along the third surface.
 2. The device accordingto claim 1, wherein the plurality of side-surface electrodes includesthree or more side-surface electrodes, and the three or moreside-surface electrodes are arranged at a uniform pitch along the thirdsurface.
 3. The device according to claim 1, wherein the plurality ofside-surface electrodes include a plurality of first side-surfaceelectrodes connected to a plurality of optical semiconductor elementsthrough a plurality of interconnects, and heights to the third surfaceare substantially uniform for the plurality of first side-surfaceelectrodes connected to the interconnects among the plurality of opticalsemiconductor elements.
 4. An optical transmission module, comprising: amodule base body; a semiconductor element; the optical transmissiondevice according to claim 1 mounted on the module base body to cause asurface of the optical transmission device where the side-surfaceelectrodes is provided and an electrode surface of the semiconductorelement to face the same direction; an inter-chip interconnectelectrically connecting at least a portion of electrodes of thesemiconductor element and at least a portion of the side-surfaceelectrodes of the optical transmission device; and an optical fiber heldin the via of the silicon substrate of the optical transmission device.5. The device according to claim 1, wherein a plurality of opticalsemiconductor elements are provided on the second surface of the siliconsubstrate, and the plurality of optical semiconductor elements areseparated from each other on the second surface of the siliconsubstrate.
 6. The device according to claim 5, wherein the secondside-surface electrode is not provided between the plurality of opticalsemiconductor elements.
 7. An optical transmission device, comprising: asilicon substrate having an optical element surface, a side surface, anda via extending toward the optical element surface from a surface on aside opposite to the optical element surface; an optical elementprovided at the optical element surface; a plurality of side-surfaceelectrodes provided at the side surface, the side-surface electrodesincluding a first side-surface electrode and a second side-surfaceelectrode, a length in a direction along the side surface of the firstside-surface electrode being different from a length in the directionalong the side surface of the second side-surface electrode; and aninterconnect provided at the optical element surface, the interconnectelectrically connecting the optical element and the first side-surfaceelectrode, the interconnect not connecting the optical element and thesecond side-surface electrode.
 8. The device according to claim 7,wherein the side-surface electrodes are provided at bottom surfaces andside surfaces of a plurality of recesses, the recesses being formed fromthe side surface to be concave to the same depth, and a length in thedirection along the side surface of the recess with the firstside-surface electrode being provided is different from a length in thedirection along the side surface of the recess with the secondside-surface electrode being provided.
 9. The device according to claim7, wherein a width of the first side-surface electrode and a width ofthe second side-surface electrode are the same in an arrangementdirection of the side-surface electrodes, and an electrode spacing isthe same for the side-surface electrodes in the arrangement direction.10. An optical transmission module, comprising: a module base body; asemiconductor element; the optical transmission device according toclaim 7 mounted on the module base body to cause a surface of theoptical transmission device where the side-surface electrodes isprovided and an electrode surface of the semiconductor element to facethe same direction; an inter-chip interconnect electrically connectingat least a portion of electrodes of the semiconductor element and atleast a portion of the side-surface electrodes of the opticaltransmission device; and an optical fiber held in the via of the siliconsubstrate of the optical transmission device.
 11. The device accordingto claim 7, wherein a plurality of optical elements are provided on theoptical element surface of the silicon substrate, and the plurality ofoptical elements are separated from each other on the optical elementsurface of the silicon substrate.
 12. The device according to claim 11,wherein the second side-surface electrode is not provided between theplurality of optical elements.
 13. A method for manufacturing an opticaltransmission device, comprising: forming an optical element at a firstmajor surface of a silicon substrate; forming a plurality of blind viasarranged along a first direction in the silicon substrate, the blindvias having openings at the first major surface and including a firstblind via and a second blind via, a depth of the second blind via beingdifferent from a depth of the first blind via; forming an electrodeinside the blind vias; forming an interconnect at the first majorsurface, the interconnect connecting the electrode and the opticalelement; and dividing the electrode inside the blind vias in a seconddirection orthogonal to the first direction by cutting the siliconsubstrate along the first direction at a position where the blind viasare arranged.
 14. The method according to claim 13, wherein an openingwidth in the second direction of the first blind via is different froman opening width in the second direction of the second blind via, andthe blind vias including the first blind via and the second blind viaare formed simultaneously by dry etching.
 15. The method according toclaim 14, wherein one end in the second direction of an opening of thefirst blind via and one end in the second direction of an opening of thesecond blind via are aligned along the first direction, and a positionof another end in the second direction of the opening of the first blindvia is shifted in the second direction with respect to a position ofanother end in the second direction of the opening of the second blindvia.